The invention relates to a sensor for determining the pressure and temperature of the air in a vehicle tire and which comprises at least one pressure and temperature sensor element arranged in a front opening of a sensor housing communicating with a tire interior, and connected with an electrical circuit.
WO 87/035 45 discloses a diaphragm box carrying an electrical contact inserted in an insulating housing screwed in a threaded hole of a wheel rim. The diaphragm box is accordingly thermally decoupled from the wheel rim, so that it takes on the temperature of the tire air, and the reference pressure in the diaphragm box is not influenced by the rim temperature. In monitoring the tire pressure, a temperature-dependent change in the tire pressure is compensated for by a corresponding change in the reference pressure in the diaphragm box by coupling the latter with the temperature of the tire air, so that when the tire pressure is too low, the electrical contact triggers a switching process and, accordingly, a warning signal which is transmitted in a wireless manner from the revolving sensor to an evaluating circuit which is stationary with respect to the vehicle.
WO 87/001.28 discloses semiconductor sensors which measure the absolute air pressure in the tire and the temperature independently of one another, arranged on an insulating plate which is received in the center of a metallic sensor housing. The housing is to be inserted into a corresponding opening of the wheel rim. In so doing, the temperature of the rim is transmitted to the sensor housing and reaches the sensors partially because of heat conduction via the insulating plate and partially due to heat radiation. Since the temperature of the wheel rim can diverge considerably from the temperature in the tire because of the proximity of the brake, but also because of the head wind, falsified values can be determined because of this thermal coupling of the sensors with the wheel rim and can trigger a false alarm and, in critical cases, can even suppress a necessary warning.